On 17/01/20 15:25, Michael S. Tsirkin wrote: > On Fri, Jan 17, 2020 at 02:58:47PM +0100, Paolo Bonzini wrote: >> On 17/01/20 14:40, Michael S. Tsirkin wrote: >>> We don't really need v2 just to add a field. Compatibility is maintained >>> using feature bits. Adding that is a subject for another patch. >>> But I'm not sure I understand why does remote need to know about alignment. >>> This patch seems to handle it locally ... >> >> Because the remote vhost here will not be able to use the synic regions. >> If it did, it would have the same overlap problem as vhost-kernel. >> >> The alignment is needed because, even if you are mapping only [768k,1M) >> of a 2M hugepage, you need to mmap [0,2M). You can then discard the >> rest, but IIUC if you only mmap [768k,1M) then the kernel will fail the >> mmap. > > So right now remote will query the fd passed to get the alignment.
It should, but will it? It's not in the spec and I assume QEMU is doing this alignment work because some server is not doing it. But indeed we could use a feature bit to say "don't worry I will be doing the right thing". Paolo > You are basically saying it's not enough in some cases? >
